CVE-2020-25674 in ImageMagick
Summary
by MITRE • 12/09/2020
WriteOnePNGImage() from coders/png.c (the PNG coder) has a for loop with an improper exit condition that can allow an out-of-bounds READ via heap-buffer-overflow. This occurs because it is possible for the colormap to have less than 256 valid values but the loop condition will loop 256 times, attempting to pass invalid colormap data to the event logger. The patch replaces the hardcoded 256 value with a call to MagickMin() to ensure the proper value is used. This could impact application availability when a specially crafted input file is processed by ImageMagick. This flaw affects ImageMagick versions prior to 7.0.8-68.
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Analysis
by VulDB Data Team • 12/14/2020
The vulnerability identified as CVE-2020-25674 represents a critical heap-buffer-overflow issue within ImageMagick's PNG image processing functionality. This flaw exists in the WriteOnePNGImage() function located in the coders/png.c file, where a for loop executes with an incorrect termination condition that directly leads to out-of-bounds memory access. The vulnerability stems from a fundamental mismatch between the expected and actual colormap data structure, where the code assumes a fixed 256-element colormap regardless of the actual data content. This improper loop condition creates a scenario where the code attempts to read beyond the allocated memory boundaries when processing PNG files with colormaps containing fewer than 256 valid entries.
The technical implementation of this vulnerability manifests through a classic buffer overflow condition that operates at the heap memory level, making it particularly dangerous for applications that process untrusted image files. The flaw specifically occurs when the loop iterates 256 times regardless of the actual colormap size, causing the system to access invalid memory locations and potentially pass garbage data to the event logging mechanism. This behavior creates multiple attack vectors since the event logger receives malformed data that could trigger additional memory corruption issues or enable attackers to infer memory layout information. The vulnerability directly maps to CWE-125, which defines out-of-bounds read conditions in software systems, and also aligns with ATT&CK technique T1203, which covers execution through input manipulation attacks.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially compromise application availability and system stability. When a maliciously crafted PNG file is processed by ImageMagick versions prior to 7.0.8-68, the heap-buffer-overflow condition can cause application crashes, denial of service scenarios, or even arbitrary code execution in certain environments. The vulnerability affects a wide range of applications that rely on ImageMagick for image processing, including web applications, content management systems, and digital asset management platforms. The patched version addresses this issue by implementing a dynamic value check using MagickMin() function, which properly calculates the minimum between the fixed 256 value and the actual colormap size, ensuring that loop iterations match the available data structure dimensions. This remediation approach aligns with secure coding practices recommended by both CWE guidelines and industry security standards, specifically addressing the root cause rather than merely masking symptoms through superficial fixes.
Organizations utilizing ImageMagick in their infrastructure should prioritize immediate patching of affected systems, particularly those handling untrusted image inputs from external sources. The vulnerability demonstrates the importance of proper input validation and boundary checking in image processing libraries, where malformed file structures can lead to severe security consequences. Security teams should implement monitoring for any unusual application behavior or crashes during image processing operations, as these could indicate exploitation attempts. The fix implemented in version 7.0.8-68 serves as a model for secure coding practices in memory management, emphasizing the need for dynamic boundary calculations rather than hardcoded assumptions about data structure sizes. This vulnerability underscores the critical nature of image processing security in modern applications and the potential for seemingly minor coding errors to create significant systemic risks.